The present invention relates to a resin multilayer molding method and a multilayer molding device in which a skin material having a resin decorating layer on a surface and a core-material resin are integrally molded in a mold.
Recently, for resin molded products for use in automobile, household appliances, building materials, and the like, in order to enhance a surface decorative quality by applying added values such as decorativeness, good feel, cushioning properties, and the like and to reduce costs by saving molding processes, resin multilayer molding has been performed in which a decorating skin material having surface decorating performance such as the decorativeness, the good feel, the cushioning properties, and the like is integrally formed on a surface of a core resin using injection molding or press molding as described later in a mold simultaneously with molding of the core resin.
After the decorating skin material is set between opened mold pieces, in a clamped sate in which a clamping force is exerted by closing the mold or in a clamped state in which a specified mold open quantity is kept between the mold pieces, a mold cavity space formed by the decorating skin material and the mold is filled with a core material or molten resin by an injection device, a resin supply unit, or the like. After the filling of the core-material resin, the mold is loaded with a follow-up pressure by the injection device or the clamping device to integrally mold the decorating skin material and the core-material resin, and the mold is opened after an elapse of a predetermined cooling time to take a molded product therefrom.
However, the decorating skin material is largely damaged by loading of high temperature and pressure by the core-material resin from when the mold is filled with the core material or molten resin till the mold is opened to take out the molded product. A problem is caused that even when the decorating skin material with a foaming layer laminated on its back surface is used aiming at, for example, softness and cushioning properties, the foaming layer collapses during molding, and the softness, the cushioning properties, or another expected surface decorating performance cannot be obtained.
Another problem is caused that even when the decorating skin material provided with a gigging layer on its surface is used aiming at, for example, good feel and high grading, the gigging layer falls during molding, and the good feel, the high grading, or another expected surface decorating performance cannot be obtained.
Further problem is caused that even when the decorating skin material with a printed or painted layer laminated on its surface is used aiming at, for example, decorativeness or painting properties, microfine scratches made in the manufacture process of the skin material or microfine strains made at the time of deformation along a mold configuration during molding cannot be avoided, which results in surface defects such as tarnish, color shading, and the like. The decorativeness, the painting properties, or another expected surface decorating performance cannot be obtained.
As aforementioned, even when the decorating skin material is used for the purpose of enhancement of the added values such as decorativeness, good feel, cushioning properties, and the like, the originally targeted surface decorating performance cannot be obtained.
Means for solving the above-mentioned problems include a method in which a decorating skin material with a film having heat/pressure resistance or another protective layer laminated thereon is used. The method is designed to moderate influences of heat and pressure loads from the core-material resin during molding with the protective layer, but the manufacture cost of the decorating skin material is increased, the decorating skin material is only incompletely protected, and the target surface decorating performance cannot be satisfied.
As another means for solving the above-mentioned problem, in the case where the printed or painted layer is laminated on the surface of the decorating skin material aiming at decorativeness and painting properties, the decorating skin material is outlined/performed into a molded product configuration at a high temperature before molding. In this method, in the preforming process at the high temperature, the microfine scratches made in the manufacture process of the skin material or the microfine strains made at the time of deformation along the mold configuration during molding can be avoided to some degree, but incompletely. Furthermore, since the preforming process is added and a separate preforming facility is necessary, the cost of resin multilayer molding and the space for performing the molding are increased.
As new means for solving the above-mentioned problems, Japanese Patent Application Laid-open No. 150740/1984 proposes a low-pressure molding method in which the pressure loaded to the decorating skin material is minimized during the resin multilayer molding using press molding. Moreover, for example, Japanese Patent Application Laid-open No. 297489/1994 proposes a molding method in which the temperature of core-material molten resin is lowered, the pressure loaded on the decorating skin material is reduced, and the product of the pressure loaded on the decorating skin material during molding and pressure loaded time is further minimized. Both proposals are designed to suppress the damage of the decorating skin material being molded by reducing influences of pressure and heat loaded on the decorating skin material.
However, even if the damage of the decorating skin material can be suppressed by reducing the pressure loaded on the decorating skin material or reducing the product of pressure and time, a moldable, necessary minimum pressure exists for molding of the core-material resin. Consequently, a shortage of molding pressure of the core-material resin causes deformation, warpage, short shot, or other molding defects in view of products.
Moreover, in the method in which the temperature of the core-material molten resin is lowered, since the fluidity of the core-material resin is extremely lowered, the pressure at the time of molding of the core-material resin is extremely lowered, the pressure at the time of molding of the core-material molten resin (filling and flowing pressures) is inevitably enlarged, and the pressure loaded on the decorating skin material fails to drop. As a result, the molding method is a contradictory (actually invalid) proposal. Even if the method can be realized, the shortage of molding pressure of the core-material resin causes deformation, warpage, short shot, or other molding defects in view of products.
To perform molding by minimizing the loaded pressure and heat influences is certainly desirable in order to control the damage of the decorating skin material during molding, but this is a molding condition in which molding cannot be performed in view of the moldability of the core-material resin. Specifically, in the resin multilayer molding of resin using the decorating skin material, contradictory molding controls for preventing the decorating skin material from being damaged and for enhancing the moldability of the core-material resin have to be simultaneously performed during molding. Not only in the case where the conventional injection molding and press molding are used, but also in the molding control simply using the proposed low-pressure molding, molding cannot be performed with both controls being compatible.
Therefore, an object of the present invention is to provide a resin multilayer molding method and a multilayer molding device which can solve the conventional problems described above.
Another object of the present invention is to provide a resin multilayer molding method and a multilayer molding device which can supply remarkably high-quality resin multilayer molded products stably at low cost without impairing surface decorating performance.